private void txtTelefon_Leave(object sender, EventArgs e)
        {
            String t = @"\+381\W\d{2}\W\d{6,7}";
            //match + 3digits space 2digits space 7digits

            Regex r = new Regex(t);

            Match m = r.Match(txtTelefon.Text);
            if (!m.Success)
            {
                MessageBox.Show("Pogresno unet broj!", "Obavestenje",
                    MessageBoxButtons.OK, MessageBoxIcon.Information);
                txtTelefon.SelectAll();
                txtTelefon.Focus();
            }

        }